Change your subscription plan in iOS
To modify your subscription, you need to go to this link from your iPhone or iPad: https://apps.apple.com/account/subscriptions . You will then be able to modify the active subscriptions of your iTunes account. Note that if you switch from a yearly plan to a monthly plan the change will be effective after your current yearly subscription expires.
Alternatively you can manage your subscription from your Mojo App, go to your "Pro" tab and click on "Manage subscription". You will then be able to switch your current plan, cancel your subscription or disable auto-renewal.